DEGREE PROJECT IN VEHICLE ENGINEERING, SECOND CYCLE, 30 CREDITS STOCKHOLM, SWEDEN 2020 Modelling and simulations of window attachments for a surface warfare ship MOHAMMAD MEKDADI KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF ENGINEERING SCIENCES Modelling and simulations of window attachments for a surface warfare ship Mohammad Mekdadi <[email protected]> KTH Royal Institute of Technology Examiner - Associate Professor Per Wennhage, KTH Supervisor - Dan Eld, FMV Master of Science Thesis Stockholm, Sweden, 2020 Abstract In recent years it has been discovered that the window installations on the Visby class corvette are prone to break. The aim of this report is to perform a structural analysis of three different window installations. Thus, to find which window installation minimizes the risk of leaks and cracks in the attachment connecting the window glass and the hull. The three window installations consist of the existing window installation and one of SAAB Kockums alternative solutions installed in two different ways, with and without an additional damping mass. The model that will be used in the simulations will consist of a rectangular shaped carbon fibre composite sandwich plate that represents the side structure of the maneuver deck. Furthermore, it will include three windows where only the middle positioned window will contain the given installation details in order to reduce the complexity of both the modelling and the simulations. Three load cases were simulated in ANSYS Workbench. The first load case called "hogging" consisted of a bending moment along the vertical sides of the model. The second load case called "slamming" consisted of a vertical force pointing upwards along the bottom of the model. Lastly, a torsion load case was simulated. In all load cases the existing window installation were subjected to the largest strains along the inner edges of the attachment. In the slamming load case, the alternative solution without the double damping mass was exposed to least strains around the inner edges of attachment compared to the other window installations. For the hogging and the torsion load case the alternative solution with double damping mass produced least strains around the inner edges of the attachment. But the alternative solution without the double damping mass was also able to reduce the strains around the inner edges compared to the existing window installation. In conclusion, the alternative solution without an additional damping mass is in overall minimizing the strains along the inner edges of the attachment in which the most leaks and cracks have been observed. It has especially been efficient in reducing strains in the slamming load case. Even though the window installation with an additional damping mass best withstands hogging and torsion, the slamming load case is the most common scenario. Therefore, the window installation that best withstands the slamming load case should be prioritized. Thus, the alternative window installation without the additional damping mass is the best alternative because it best withstands slamming but also reduces the strains along the inner edges compared to the existing window installation in the other load cases. Sammanfattning Under de senaste åren har det upptäckts att fönsterinstallationerna på Visby-klasskorvetten har en benägenhet att brista. Syftet med denna studie är att utföra en hållfasthetsanalys på tre oli- ka fönsterinstallationer. Därav är målet att hitta den fönsterinstallation som minimerar risken för läckor samt sprickor i smygskarven som kopplar fönsterglaset med skrovet. De tre fönsterinstalla- tionerna består av den befintliga fönsterinstallationen samt en av SAAB Kockums lösningsförslag installerat på två olika sätt, med och utan dubbel dämpningsmassa. Modellen som ska användas i simuleringarna kommer att bestå av en rektangulär skiva bestående av en sandwichkonstruktion med lamineringar av kolfiberkomposit. Skivan ska motsvara sidan av manöverbryggan. Modellen in- kluderar tre fönster där endast mittenfönstret kommer att modelleras med de givna detaljerna på samtliga fönsterinstallationerna. Detta för att förenkla både modelleringen och simuleringarna. Tre olika lastfall kommer att simuleras i ANSYS Workbench. Det första lastfallet kallas "hoggingsom kommer utgöras av ett böjmoment längs de vertikala sidorna om modellen. Det andra lastfallet kallas slammingöch består av en vertikal kraft riktad uppåt längs modellens undersida. Slutligen, består det sista lastfallet av en kraft på respektive vertikala sida längs modellen som ska ge upphov till en vridning på modellen. I samtliga lastfall gav den befintliga fönsterinstallationen upphov till störst töjningar längs innerkanterna på smygskarven (kanterna närmast fönsterglaset). I slamming lastfallet gav lösningsförslaget utan dubbel dämpningsmassa upphov till minst töjningar längs inner- kanterna på smygskarven jämfört med övriga fönsterinstallationer. I hogging och vridning lastfallen gav lösningsförslaget med dubbel dämpningsmassa upphov till minst töjningar längs innerkanterna på smygskarven. Även lösningsförslaget utan dämpningsmassa lyckades dämpa töjningarna längs in- nerkanterna på smygskarven jämfört med den befintliga fönsterinstallationen. Sammanfattningsvis har lösningsförslaget utan dubbel dämpningsmassa i helhet minskat töjningarna längs innerkanterna på smygskarven där de flesta läckor och sprickor har observerats. Framförallt har lösningsförslaget varit effektiv i slamming lastfallet. Även fast lösningsförslaget med dubbel dämpningsmassa bäst mot- står hogging och vridning, är slamming lastfallet det mest förekommande lastfallet. Därför bör den fönsterinstallation som bäst dämpar töjningarna vid slamming prioriteras. Därav är lösningsförslaget utan dubbel dämpningsmassa det bästa alternativet då den är effektivast mot slamming samt att den reducerar töjningarna kring innerkanterna på smygskarven jämfört med befintliga fönsterinstal- lationen i resterande lastfall. Acknowledgement I would like to thank a number of persons who helped and encouraged me during the time of this project. First, I would like to thank Dan Eld, my supervisor at FMV for giving me the opportunity to write my thesis at FMV that has been very interesting and helped me gaining new experiences and develop my engineering skills. I am very grateful for his support and guidance throughout the project that has helped me moving forward. I would also like to thank my supervisor and examiner at KTH Royal Institute of Tecknology Professor Per Wennhage for providing me with help and advice regarding the theory and the software used in this project. He never hesitated to have meetings and discuss questions that arose during the project which was greatly appreciated. Furthermore, I would like to thank PhD Gustav Hultgren for his advice in ANSYS. Lastly, I want to thank my loving family and my friends for their support and for always standing by my side throughout my studies at KTH. Without them none of this would have been possible. Contents 1 Introduction 1 1.1 Background . 1 1.2 Problem formulation . 1 1.3 Initial Assumptions and Simplifications . 2 2 Theory 3 2.1 Structural Loads . 3 2.1.1 Longitudinal strength loads . 3 2.1.2 Hogging and Sagging . 4 2.1.3 Slamming . 6 2.2 Sandwich Structures . 7 2.3 FEM................................................. 8 2.3.1 ANSYS Workbench . 8 2.3.2 Large deflections . 9 3 The Structure of Corvette Visby 10 3.1 The Hull Structure of HMS Visby . 10 3.2 Reinforcements . 11 3.3 The existing window installation . 13 3.3.1 The window attachment . 13 3.3.2 Sikaflex . 14 3.3.3 Silicone Seal . 15 3.4 Alternative window installations . 15 4 Methodology 17 4.1 The model of the maneuver deck . 17 4.1.1 3D-model of the hull . 17 4.1.2 3D-Model of the Reinforcement . 18 4.1.3 Fibre Orientation . 19 4.2 Modelling of the Existing Window Installation . 20 4.2.1 Meshing model . 23 4.3 Modelling of Alternative Window Installations . 24 4.3.1 Meshing model . 24 4.4 Load Cases and Boundary Conditions . 25 4.4.1 Hogging load case . 25 4.4.2 Slamming load case . 26 4.4.3 Torsion load case . 27 5 Results and analysis 28 5.1 Hogging load case . 28 5.1.1 Existing window installation . 29 5.1.2 Alternative window installation (without double damping mass) . 30 5.1.3 Alternative window installation (with double damping mass) . 31 5.2 Slamming load case . 32 5.2.1 Existing window installation . 32 5.2.2 Alternative window installation (without double damping mass) . 33 5.2.3 Alternative window installation (with double damping mass) . 34 5.3 Torsion load case . 35 5.3.1 Existing window installation . 35 5.3.2 Alternative window installation (without double damping mass) . 36 5.3.3 Alternative window installation (with double damping mass) . 37 5.4 Summary of Results . 38 6 Discussion 39 7 Conclusion 41 8 Future Work 42 References 43 Appendix A A-1 A.1 Dimensions of the 3D-model of the hull . A-1 Appendix B B-1 B.1 Sikaflex 265 glue strings in the attachment of the alternative window installations subjected to different load cases . B-1 1 1 Introduction 1.1 Background The modern corvettes were used back in World War II. The advantages were their smaller size combined with improved maneuverability. A corvette can be described as a small warfare ship which typically weights between 500 tons up to 3000 tons[1]. Sweden is one of the countries that still are operating corvettes today. The latest class of corvette in Sweden is the Visby class corvette, see figure 1. The Visby class corvette was built for the Royal Swedish Navy and constructed by SAAB Kockums under the lead of FMV (the Swedish Defense Materiel Administration). The first Visby class corvette, HMS Visby was delivered in December 2009. HMS Visby weights 640 tonnes (fully equipped) and its hull is entirely made of carbon fibre composite sandwich.[2] In recent years it has been discovered that the window installations on the corvette are prone to break. The attachment that connects the window with the hull is detached from the window glass over time when the corvette is operated under normal conditions. Consequently, the risk of water entering the gap between the window and the hull increases.